Electrode with redundant impedance reduction

ABSTRACT

An electrode assembly that includes an electrically conductive layer, a first impedance reduction system, and a second impedance reduction system. The electrically conductive layer forms an electrode portion of the electrode assembly and a first surface to be placed adjacent a person&#39;s skin. The first impedance reduction system is configured to dispense a first amount of an electrically conductive gel onto the first surface of the electrically conductive layer in response to a first activation signal. The second impedance reduction system is configured to dispense a second amount of the electrically conductive gel onto the first surface of the electrically to conductive layer in response to a second activation signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §120 as acontinuation of U.S. application Ser. No. 13/315,937 titled “ELECTRODEWITH REDUNDANT IMPEDANCE REDUCTION” filed Dec. 9, 2011, which claimspriority under 35 U.S.C. §120 as a continuation of International PatentApplication Serial No. PCT/US2011/063931, titled “ELECTRODE WITHREDUNDANT IMPEDANCE REDUCTION” filed Dec. 8, 2011, which claims priorityunder 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No.61/421,283 titled “ELECTRODE WITH REDUNDANT IMPEDANCE REDUCTION” filedDec. 9, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to medical electrodes, and moreparticularly, to a medical electrode with redundant impedance reductionsystems that may be used with a wearable medical device, such as adefibrillator.

2. Discussion of Related Art

Cardiac arrest and other cardiac health ailments are a major cause ofdeath worldwide. Various resuscitation efforts aim to maintain thebody's circulatory and respiratory systems during cardiac arrest in anattempt to save the life of the victim. The sooner these resuscitationefforts begin, the better the victim's chances of survival. Theseefforts are expensive and have a limited success rate, and cardiacarrest, among other conditions, continues to claim the lives of victims.

To protect against cardiac arrest and other cardiac health ailments,some at-risk patients may use a wearable defibrillator, such as theLifeVest® wearable cardioverter defibrillator available from ZollMedical Corporation of Chelmsford, Mass. To remain protected, thepatient wears the device nearly continuously while going about theirnormal daily activities, while awake, and while asleep.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, an electrodeassembly is provided. The electrode assembly comprises an electricallyconductive layer that forms an electrode portion of the electrodeassembly, a first impedance reduction system, and a second impedancereduction system. The electrically conductive layer has a first surfaceto be placed adjacent a person's skin. The first impedance reductionsystem is configured to dispense a first amount of a first electricallyconductive gel onto the first surface of the electrically conductivelayer in response to a first activation signal, and the second impedancereduction system is configured to to dispense a second amount of asecond electrically conductive gel onto the first surface of theelectrically conductive layer in response to a second activation signal.

In accordance with one embodiment, the first activation signal and thesecond activation signal are based upon the same signal. In accordancewith another embodiment, the first activation signal is distinct fromthe second activation signal.

In accordance with an aspect of the present invention, the secondimpedance reduction system is configured to dispense the second amountof the second electrically conductive gel onto the first surface of theelectrically conductive layer in response to the second activationsignal and independent of whether the first impedance reduction systemdispenses the first amount of the first electrically conductive gel onthe first surface of the electrically conductive layer in response tothe first activation signal.

In accordance with one embodiment, the first impedance reduction systemis similar in construction to the second impedance reduction system.

In accordance with one embodiment, the electrically conductive layer hasa plurality of apertures formed there through, the plurality ofapertures including a first plurality of apertures and a secondplurality of apertures. In accordance with this embodiment, the firstimpedance reduction system is configured to dispense the first amount ofthe first electrically conductive gel through the first plurality ofapertures and onto the first surface of the electrically conductivelayer in response to the first activation signal, and the secondimpedance reduction system is configured to dispense the second amountof the second electrically conductive gel through the second pluralityof apertures and onto the first surface of the electrically conductivelayer in response to the second activation signal. In one embodiment,the first electrically conducting gel and the second electricallyconducting gel are the same type of electrically conducting gel.

In accordance with another aspect of the present invention, an electrodeassembly is provided. The electrode assembly comprises an electricallyconductive layer, a first plurality of gel reservoirs, a secondplurality of gel reservoirs, a first fluid channel, a second fluidchannel, a first fluid pressure source, and a second fluid pressuresource. The electrically conductive layer has a plurality of aperturesformed to therein, the plurality of apertures including a firstplurality of apertures and a second plurality of apertures. The firstplurality of gel reservoirs each contain a first electrically conductivegel, each respective gel reservoir of the first plurality of gelreservoirs having an outlet to fluidly communicate with a respectiveaperture of the first plurality of apertures. The second plurality ofgel reservoirs each contain a second electrically conductive gel, eachrespective gel reservoir of the second plurality of gel reservoirshaving an outlet to fluidly communicate with a respective aperture ofthe second plurality of apertures. The first fluid channel is in fluidcommunication with each of the first plurality of gel reservoirs, andthe second fluid channel is in fluid communication with each of thesecond plurality of gel reservoirs. The first fluid pressure source isin fluid communication with the first fluid channel and configured toreceive a first activation signal and force a first fluid under pressureinto the first fluid channel in response to the first activation signal,and the second fluid pressure source is in fluid communication with thesecond fluid channel and configured to receive a second activationsignal and force a second fluid under pressure into the second fluidchannel in response to the second activation signal.

In accordance with one embodiment, the outlet of each of the firstplurality of gel reservoirs and the outlet of each of the secondplurality of gel reservoirs is sealed by a membrane that is constructedto rupture in response to the pressure of the first fluid and the secondfluid, respectively.

In accordance with one embodiment, the first activation signal and thesecond activation signal are based upon the same signal. In anotherembodiment, the first activation signal is distinct from the secondactivation signal.

In accordance with another aspect of the present invention, an electrodeassembly is provided that comprises at least one ECG sensing electrode,a therapy electrode, a first impedance reduction system and a secondimpedance reduction system. The at least one ECG sensing electrode isconfigured to monitor an ECG signal of a patient and the therapyelectrode is configured to deliver a defibrillating shock to thepatient. The first impedance reduction system is configured to reduce anto impedance between the therapy electrode and the patient in responseto a first activation signal, and the second impedance reduction systemis configured to reduce the impedance between the therapy electrode andthe patient in response to a second activation signal. In accordancewith one embodiment, the at least one ECG sensing electrode iselectrically insulated from the therapy electrode.

In accordance with one embodiment, the at least one ECG sensingelectrode includes a plurality of ECG sensing electrodes. In accordancewith a further aspect of this embodiment, each of the plurality of ECGsensing electrodes is electrically insulated from the therapy electrode.

In accordance with one embodiment, the electrode assembly furthercomprises at least one additional sensor configured to monitor aphysiological parameter of the patient that is other than the ECG signalof the patient.

In accordance with one embodiment, the first activation signal and thesecond activation signal are based upon the same signal, and the firstimpedance reduction system is similar in construction to the secondimpedance reduction system.

In accordance with one embodiment, the therapy electrode includes anelectrically conductive layer having a first surface to be placedadjacent a person's skin and a plurality of apertures formed through theelectrically conductive layer. The plurality of apertures includes afirst plurality of apertures and a second plurality of apertures. Thefirst impedance reduction system is configured to dispense a firstamount of a first electrically conductive gel through the firstplurality of apertures and onto the first surface of the electricallyconductive layer in response to the first activation signal, and thesecond impedance reduction system is configured to dispense a secondamount of a second electrically conductive gel through the secondplurality of apertures and onto the first surface of the electricallyconductive layer in response to the second activation signal.

In accordance with another aspect of the present invention, a method ofreducing impedance between an electrode and a patient's skin isprovided. The method comprises acts of sending a first activation signalto a first impedance reduction system configured to dispense a firstamount of a first electrically conducting gel onto a surface of theelectrode that is configured to be disposed to adjacent the patient'sskin, and sending a second activation signal to a second impedancereduction system configured to dispense a second amount of a secondelectrically conducting gel onto the surface of the electrode that isconfigured to be disposed adjacent the patient's skin, the secondimpedance reduction system being distinct from the first impedancereduction system.

In accordance with one embodiment, the method further comprises an actof determining whether the first impedance reduction system dispensedthe first amount of the first electrically conducting gel onto thesurface of the electrode, wherein the act of sending the secondactivation signal to the second impedance reduction system is performedin response to a determination that the first impedance reduction systemdid not dispense the first amount of the first electrically conductinggel onto the surface of the electrode. In accordance with oneembodiment, the act of sending the second activation signal is performedsubsequent to the act of sending the first activation signal. In analternative embodiment, the act of sending the second activation signalis performed substantially simultaneously with the act sending the firstactivation signal.

Still other aspects, embodiment, and advantages of these exemplaryaspects and embodiments are discussed in detail below. Moreover, it isto be understood that both the foregoing information and the followingdetailed description are merely illustrative examples of various aspectsand embodiments of the present invention, and are intended to provide anoverview or framework for understanding the nature and character of theclaimed aspects and embodiments. Any embodiment disclosed herein may becombined with any other embodiment in any manner consistent with aspectsof the present invention disclosed herein, and references to “anembodiment,” “some embodiments,” “an alternate embodiment,” “variousembodiments,” “one embodiment,” “at least one embodiment,” “this andother embodiments” or the like are not necessarily mutually exclusiveand are intended to indicate that a particular feature, structure, orcharacteristic described in connection with the embodiment may beincluded in at least one embodiment. The appearance of such terms hereinis not necessarily all referring to the same embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 illustrates a wearable medical device, such as a wearabledefibrillator;

FIG. 2 a is a plan view of an electrode portion of a therapy electrodeassembly that may be used with the wearable medical device illustratedin FIG. 1;

FIG. 2 b is a functional block diagram of an impedance reduction systemthat may be included in the electrode portion of FIG. 2 a;

FIG. 3 is a functional block diagram of a redundant impedance reductionsystem in accordance with an aspect of the present invention;

FIG. 4 is a schematic diagram of an electrode assembly that includes ECGsensing electrodes, a therapy electrode, and redundant impedancereduction systems in accordance with another aspect of the presentinvention; and

FIG. 5 illustrates the manner in which the electrode assembly of FIG. 4may be worn on the body of a patient.

DETAILED DESCRIPTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” “having,” “containing,”“involving,” and variations thereof herein is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems.

FIG. 1 illustrates a wearable medical device, such as a LifeVest®wearable cardioverter defibrillator available from Zoll MedicalCorporation of Chelmsford, Mass. As shown, the wearable medical device100 includes a harness 110 having a pair of shoulder straps and a beltthat is worn about the torso of a patient. The harness 110 is typicallymade from a material, such as cotton, that is breathable, and unlikelyto cause skin irritation, even when worn for prolonged periods of time.The wearable medical device 100 includes a plurality of ECG sensingelectrodes 112 that are attached to the harness 110 at various positionsabout the patient's body and electrically coupled to a control unit 120via a connection pod 130. The plurality of ECG sensing electrodes 112,which may be dry-sensing capacitance electrodes, are used by the controlunit 120 to monitor the cardiac function of the patient and generallyinclude a front/back pair of ECG sensing electrodes and a side/side pairof ECG sensing electrodes. Additional ECG sensing electrodes may beprovided, and the plurality of ECG sensing electrodes 112 may bedisposed at varying locations about the patient's body.

The wearable medical device 100 also includes a plurality of therapyelectrodes 114 that are electrically coupled to the control unit 120 viathe connection pod 130 and which are capable of delivering one or moretherapeutic defibrillating shocks to the body of the patient, if it isdetermined that such treatment is warranted. As shown, the plurality oftherapy electrodes 114 includes a first therapy electrode 114 a that isdisposed on the front of the patient's torso and a second therapyelectrode 114 b that is disposed on the back of the patient's torso. Thesecond therapy electrode 114 b includes a pair of therapy electrodesthat are electrically coupled together and act as the second therapyelectrode 114 b. The use of two therapy electrodes 114 a, 114 b permitsa biphasic shock to be delivered to the body of the patient, such that afirst of the two therapy electrodes can deliver a first phase of thebiphasic shock with the other therapy electrode acting as a return, andthe other therapy electrode can deliver the second phase of the biphasicshock with the first therapy electrode acting as the return. Theconnection pod 130 electrically couples the plurality of ECG sensingelectrodes 112 and the plurality of therapy electrodes 114 to thecontrol unit 120, and may include electronic circuitry. For example, inone implementation the connection pod 130 includes signal acquisitioncircuitry, such as a plurality of differential amplifiers to receive ECGsignals from different ones of the plurality of ECG sensing electrodes112 and to provide a differential ECG signal to the control unit 120based on the difference therebetween. The connection pod 130 may also toinclude other electronic circuitry, such as a motion sensor oraccelerometer by which patient activity may be monitored.

As shown in FIG. 1, the wearable medical device 100 also includes a userinterface pod 140 that is electrically coupled to the control unit 120.The user interface pod 140 can be attached to the patient's clothing orto the harness 110, for example, via a clip (not shown) that is attachedto a portion of the interface pod 140. Alternatively, the user interfacepod 140 may simply be held in a person's hand. In some embodiments, theuser interface pod 140 may communicate wirelessly with the control unit120, for example, using a Bluetooth®, Wireless USB, ZigBee, WirelessEthernet, GSM, or other type of communication interface. The userinterface pod 140 typically includes a number a number of buttons bywhich the patient, or a bystander can communicate with the control unit120, and a speaker by which the control unit 120 may communicate withthe patient or the bystander. For example, where the control unit 120determines that the patient is experiencing cardiac arrhythmia, thecontrol unit 120 may issue an audible alarm via a loudspeaker (notshown) on the control unit 120 and/or the user interface pod 140alerting the patient and any bystanders to the patient's medicalcondition. The control unit 120 may also instruct the patient to pressand hold one or more buttons on the control unit 120 or on the userinterface pod 140 to indicate that the patient is conscious, therebyinstructing the control unit 120 to withhold the delivery of one or moretherapeutic defibrillating shocks. If the patient does not respond, thedevice may presume that the patient is unconscious, and proceed with thetreatment sequence, culminating in the delivery of one or moredefibrillating shocks to the body of the patient. In some embodiments,the functionality of the user interface pod 140 may be integrated intothe control unit 120.

The control unit 120 generally includes at least one processor,microprocessor, or controller, such as a processor commerciallyavailable from companies such as Texas Instruments, Intel, AMD, Sun,IBM, Motorola, Freescale and ARM Holdings. In one implementation, the atleast one processor includes a power conserving processor arrangementthat comprises a general purpose processor, such as an Intel® PXA270processor and a special purpose processor, such as a Freescale DSP56311to Digital Signal Processor. Such a power conserving processorarrangement is described in co-pending application Ser. No. 12/833,096,entitled SYSTEM AND METHOD FOR CONSERVING POWER IN A MEDICAL DEVICE,filed Jul. 9, 2010 (hereinafter the “'096 application”) which isincorporated by reference herein in its entirety. The at least oneprocessor of the control unit 120 is configured to monitor the patient'smedical condition, to perform medical data logging and storage, and toprovide medical treatment to the patient in response to a detectedmedical condition, such as cardiac arrhythmia. Although not shown, thewearable medical device 100 may include additional sensors, other thanthe ECG sensing electrodes 112, capable of monitoring the physiologicalcondition or activity of the patient. For example, sensors capable ofmeasuring blood pressure, heart rate, thoracic impedance, pulse oxygenlevel, respiration rate, heart sounds, and the activity level of thepatient may also be provided.

As discussed above, to provide protection against cardiac arrest,patients that use a wearable medical device, such as a wearabledefibrillator, generally wear the device nearly continuously while theyare awake and while they are asleep. Because the wearable medical deviceis worn nearly continuously, dry electrodes are typically used for boththe plurality of ECG sensing electrodes 112 and the plurality of therapyelectrodes 114 for comfort and to prevent irritation of the patient'sskin. Where it is determined that one or more defibrillating shocks areto be delivered to the body of the patient and the patient isnon-responsive, the control unit 120 sends a signal to the plurality oftherapy electrodes 114 causing them to release an impedance reducing gelprior to delivery of one or more defibrillating shocks. The impedancereducing gel reduces the impedance between the conductive surface of thetherapy electrodes and the patient's skin, thereby improving theefficiency of the energy delivered to the patient and reducing thechance of damage (e.g., in the form of burning, reddening, or othertypes of irritation) to the patient's skin.

FIG. 2 a is a plan view of an electrode portion of a therapy electrodeassembly that includes an impedance reduction system and which may beused with a wearable medical device, such as the wearable defibrillatordescribed above with respect to FIG. 1. FIG. 2 b is a functional blockdiagram of the impedance reduction system that is to included in theelectrode portion of the therapy electrode assembly shown in FIG. 2 a.The impedance reduction system, when activated, dispenses an impedancereducing (i.e., electrically conductive) gel onto the exposed surface ofthe electrode portion of the therapy electrode assembly that, in use, isplaced most proximate to the patient's body. The electrode portion 200is a multiple layer laminated structure that includes an electricallyconductive layer (not visible in FIG. 2 a, but disposed adjacent thebottom surface of the electrode portion 200 shown in FIG. 2 a) thatforms the electrode and an impedance reduction system 201. In use, theelectrically conductive layer is disposed adjacent the patient's skin,although the conductive layer need not make direct contact with thepatient, as portions of the harness 110 (FIG. 1) and/or portions of thepatient's clothing may be present between the electrically conductivelayer and the patient's skin. As shown in FIG. 2 a, the impedancereduction system 201 is disposed on a side of the electrode portion 200(i.e., the top-side shown in FIG. 2 a) that is opposite the side onwhich the conductive layer is formed.

The impedance reduction system 201 includes a plurality of conductivegel reservoirs 210, each of which has a respective gel delivery outlet220, that are fluidly coupled to a fluid channel 230, and a fluidpressure source 240. The fluid pressure source 240 is fluidly coupled tothe fluid channel 230, and when activated by an activation signal,forces a fluid, such as Nitrogen gas, into the channel 230. Thehydraulic pressure of the fluid from the activated fluid pressure source240 in the fluid channel 230 forces the conductive gel stored in each ofthe plurality of gel reservoirs out of the plurality of gel deliveryoutlets 220 through apertures formed in the electrically conductivelayer and onto the exposed surface of the electrically conductive layerthat, in use, is placed most proximate to the patient's body. Theapertures in the electrically conductive layer are generally alignedwith the plurality of gel delivery outlets 220 so that when activated,the electrically conductive gel is dispensed onto the exposed surface ofthe electrode portion that is disposed most proximate to the patient'sbody. Further details regarding the construction of the electrodeportion 200 are described in U.S. Pat. No. 5,078,134 (hereinafter “the'134 patent”) which is incorporated herein by reference.

Applicants have appreciated that there may be instances where it wouldbe to desirable to have redundancy in the impedance reduction systemdescribed above. An electrode that incorporates redundant impedancereduction systems is now described with respect to FIGS. 3-5 below.

FIG. 3 is a functional block diagram of a redundant impedance reductionsystem that may be incorporated in an electrode assembly in accordancewith an aspect of the present invention. As shown, the redundantimpedance reduction system 300 includes at least two independentimpedance reduction systems 301, 302 similar in construction andoperation to that described previously with respect to FIGS. 2 a and 2b. Although only two impedance reduction systems 301, 302 are shown inFIG. 3, it should be appreciated that additional impedance reductionsystems may be provided.

As shown, a first impedance reduction system 301 of the at least twoimpedance reduction systems 301, 302 includes a first plurality of gelreservoirs 310 a, each containing an electrically conductive gel, witheach respective gel reservoir including a gel delivery outlet 320 a.Each of the first plurality of gel reservoirs 310 a is fluidly coupledto a first fluid channel 330 a that is, in turn, fluidly coupled to afirst fluid pressure source 340 a. The first fluid pressure source 340 ahas an input 341 a to receive a first electrical activation signal and afluid outlet 342 a that is fluidly coupled to the first fluid channel330 a. A rupturable membrane and/or a filter (not shown) may bepositioned between the fluid outlet 342 a and the first fluid channel330 a as described in the '134 patent. As described in the '134 patent,the first fluid pressure source 340 a may include a gas generatingcartridge that ignites a chemical pellet (such as a Lead Styphnateigniter and a gas generating mixture of Ammonium Dichromate andNitroguanidine) that rapidly decomposes and generates quantities of agas, such as Nitrogen. It should be appreciated that other types offluid pressure sources may be used, as the present invention is notlimited to any particular type of fluid pressure source.

In response to the first activation signal received at the input 341 aof the first fluid pressure source 340 a, a fluid, such as Nitrogen gas,is forced into the first fluid channel 330 a and then into each of thefirst plurality of gel reservoirs 310 a. The hydraulic pressure of thefluid flowing into each of the first plurality of gel reservoirs 310 aforces the electrically conductive gel contained in each gel reservoirtoward its to respective gel delivery outlet 320 a, thereby fracturing amembrane separating the gel delivery outlet from a respective apertureformed in the electrically conductive layer of the electrode portion.

The second impedance reduction system 302 of the at least two impedancereduction systems 301, 302 is similar to the first impedance reductionsystem 301 and includes a second plurality of gel reservoirs 310 b, eachcontaining an electrically conductive gel, with each respective gelreservoir including a gel delivery outlet 320 b. The electricallyconductive gel contained in the second plurality of gel reservoirs 310 bmay, but need not, be the same type of gel as that contained in thefirst plurality of gel reservoirs 310 a. For example, the electricallyconductive gel contained in the second plurality of gel reservoirs 310 bmay have a different color, or have a longer drying time than the gelcontained in the first plurality of gel reservoirs 310 a. Each of theplurality of gel reservoirs 310 b is fluidly coupled to a second fluidchannel 330 b that is, in turn, fluidly coupled to a second fluidpressure source 340 b. The second fluid pressure source 340 b has aninput 341 b to receive a second electrical activation signal and a fluidoutlet 342 b that is fluidly coupled to the second fluid channel 330 b.The second fluid pressure source 340 b may similar in construction tothe first fluid source 340 a described above.

As shown in FIG. 3, the input 341 a of the first fluid pressure source340 a may be electrically connected to the input 341 b of the secondfluid pressure source, such that a single activation signal activateseach of the at least two impedance reduction systems 301, 302substantially simultaneously. Should one of the redundant impedancereduction systems 301, 302 fail to operate (either partially orcompletely), the other can still operate to dispense conductive gel ontothe exposed surface of the electrode. The activation signal provided tothe input 341 a of the first fluid pressure source 340 a may be providedby the control unit 120 (FIG. 1) to the first fluid pressure source 340a using an electrical conductor that is physically distinct from thatwhich provides the activation signal to the input 341 b of the secondfluid pressure source 340 b to permit further redundancy, for example,should one of the electrical conductors be damaged. Alternatively, asingle electrical conductor may be provided between the control unit 120and the electrode assembly, with the single electrical to conductorbeing connected to both the input 341 a of the first fluid pressuresource 340 a and the input 341 b of the second fluid pressure source 340b.

It should be appreciated that each of the first and second pressuresources 340 a, 340 b may alternatively receive separate activationsignals, as the present invention is not limited to receiving a singleactivation signal. The separate activation signals may be sent, forexample by the control unit 120, to each of the first fluid pressuresource 340 a and the second fluid pressure source 340 b at substantiallythe same time, or at different times. For example, a first activationsignal may be provided to the input 341 a of the first fluid pressuresource 340 a at a first time, and a second activation signal may beprovided to the input 341 b of the second fluid pressure source 340 b ata second time that is subsequent to the first time. In accordance withone embodiment, the control unit 120 (FIG. 1) may send the firstactivation signal to the first fluid pressure source 340 a at a firsttime, and send the second activation signal to the second fluid pressuresource 340 b at a second and subsequent time where it is determined thatthe first impedance reduction system 301 failed to operate.Alternatively, the second activation signal may be sent to the secondfluid pressure source 340 b at a second and subsequent time even whereactivation of the first fluid pressure source 340 a is successful. Sucha subsequent activation of the second fluid pressure source 340 b wouldpermit a second deployment of conductive gel onto the exposed surface ofthe electrode and permit the electrode to maintain a high conductivitywith the patient for a longer period of time than if both impedancereduction systems 301, 302 were activated at substantially the sametime.

FIG. 4 illustrates an electrode assembly that combines one or more ECGsensing electrodes, a therapy electrode, and redundant impedancereduction systems in a single integrated electrode assembly inaccordance with a further aspect of the present invention. As shown, theelectrode assembly 400 includes a pair of ECG sensing electrodes 412 a,412 b for monitoring the cardiac function of a patient. The electrodeassembly 400 further includes a therapy electrode 414, and at least twoimpedance reduction systems 301, 302, similar to those describedpreviously with respect to FIG. 3. The pair of ECG sensing electrodes412 a, 412 b may be electrically separated from the therapy electrode414, for example, by an insulator. It should be appreciated that inother embodiments, the electrode assembly 400 may include only a singleECG sensing electrode, while in other embodiments, more than two ECGsensing electrodes may be provided. In such alternative embodiments, thenumber and placement of ECG sensing electrodes and may vary from thatshown in FIG. 4. In yet a further embodiment, the integrated electrodeassembly can include additional sensors 416, other than the one or moreECG sensing electrodes and the therapy electrode, that are capable ofmonitoring other physiological parameters of a patient, such as bloodpressure, heart rate, thoracic impedance, pulse oxygen level,respiration rate, heart sounds, etc.

The electrode assembly 400 may be worn on the patient's body such thatone of the pair of ECG sensing electrodes 412 a, 412 b is disposedapproximately in the center of the patient's torso, and the other of thepair of ECG sensing electrodes 412 a, 412 b is disposed on the side ofthe patient's torso. For example, as shown in FIG. 5, the electrodeassembly 400 may be worn on the front of the patient's torso, so thatthe ECG sensing electrode 412 a is disposed approximately in the centerof the patient's chest, and the other ECG sensing electrode 412 b isdisposed on the patient's side. A second electrode assembly 400′ may beworn on the back of the patient's torso to provide a second pair of ECGsensing electrodes 412 a′, 412 b′, so that one of the ECG sensingelectrodes (e.g., ECG sensing electrode 412 a′) of the second pair ofECG sensing electrodes 400′ is disposed approximately in the center ofthe patient's back, and the other ECG sensing electrode (e.g., ECGsensing electrode 412 b′) of the second pair of ECG sensing electrodes400′ is disposed on the patient's side opposite the other ECG sensingelectrode (e.g., ECG sensing electrode 412 b) of the first pair of ECGsensing electrodes 412 a, 412 b, as shown in FIG. 5. Such an arrangementprovides a front-to-back pairing of ECG sensing electrodes (e.g., 412 a,412 a′) and a side-to-side pairing of ECG sensing electrodes (e.g., 412b, 412 b′). It should be appreciated that other placements for the firstelectrode assembly 400 and the second electrode assembly 400′ mayalternatively be used. For example, the first electrode assembly 400 maybe placed on one side of the patient's torso, and the second electrodeassembly 400′ placed on the other side of the patient's torso to provideside-to-side pairings of ECG sensing electrodes.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the scope of theinvention. Accordingly, the foregoing description and drawings are byway of example only.

What is claimed is:
 1. A method of reducing impedance between adefibrillation electrode and a patient's skin, comprising acts of:sending a first activation signal to a first impedance reduction systemconfigured to dispense a first amount of a first electrically conductivegel onto a surface of the defibrillation electrode that is configured tobe disposed adjacent the patient's skin; and sending a second activationsignal that is distinct from the first activation signal to a secondimpedance reduction system configured to dispense a second amount of asecond electrically conductive gel onto the surface of thedefibrillation electrode that is configured to be disposed adjacent thepatient's skin, the second impedance reduction system being distinctfrom the first impedance reduction system and independently operable ofthe first impedance reduction system.
 2. The method of claim 1, whereinthe act of sending the second activation signal is performedsubstantially simultaneously with the act of sending the firstactivation signal.
 3. The method of claim 1, wherein the act of sendingthe second activation signal is performed subsequent to the act ofsending the first activation signal.
 4. The method of claim 1, whereinthe act of sending the first activation signal is performed at a firsttime, and wherein the act of sending the second activation signal isperformed at a second time that is substantially after the first time tomaintain the impedance between the defibrillation electrode andpatient's skin in a reduced state for an extended duration.
 5. Themethod of claim 4, wherein the second electrically conductive gel has alonger drying time than the first electrically conducting gel.
 6. Themethod of claim 1, further comprising an act of determining whether thefirst impedance reduction system dispensed the first amount of the firstelectrically conductive gel onto the surface of the defibrillationelectrode, wherein the act of sending the second activation signal tothe second impedance reduction system is performed in response to adetermination that the first impedance reduction system did not dispensethe first amount of the first electrically conductive gel onto thesurface of the defibrillation electrode.
 7. The method of claim 1,wherein the act of sending the second activation signal to is performedindependent of whether the first impedance reduction system dispensedthe first amount of the first electrically conductive gel onto thesurface of the defibrillation electrode.